Adsorption refrigeration systems are well known in the field of refrigeration and particularly cryogenics, for providing very low temperatures in a region such as a chamber. Adsorption refrigeration systems operate by the provision of an amount of liquid coolant within a chamber to be cooled. This is placed in gaseous communication with an amount of adsorbing material such as charcoal, the entire system being closed such that the amount of coolant within the system remains constant. Typically the coolant in liquid form is obtained by condensation of gaseous coolant in contact with the cold walls of a member pre-cooled by an external source. This is performed in many conventional adsorption refrigeration systems by the use of a “1K pot”.
A second and alternative method of obtaining liquid coolant uses an expansion process, in which case the coolant is decompressed from a high pressure under adiabatic conditions. This decompression causes liquefaction of the gas thereby generating the liquid coolant. The adsorption material of the system is arranged to adsorb the gas above the liquid coolant such that further evaporation of the liquid occurs due to the corresponding reduction in the pressure. The latent heat of evaporation causes a reduction in the temperature of the system.
One problem with using such systems is that they are effectively “single-shot”, meaning that they may only be operated for a predetermined period of time which, in commercial systems, may be a number of hours.
Adsorption systems are advantageous in that they are relatively simple devices which can be re-charged by simply heating the adsorption material so as to cause desorption of the coolant gas thereby returning it to the gaseous state. Upon sufficient subsequent cooling, the adsorption material can once more be reused. Since the systems are “closed”, there is no loss of coolant and there are no moving parts. This is beneficial in that low temperature experiments can be performed at low levels of vibration for many hours.
In order to address the relatively short time period “single-shot” nature of such systems, we have previously devised a method of operating an adsorption refrigeration system in accordance with our earlier European patent application EP1387133A, the disclosure of which is hereby incorporated by reference in its entirety into the present disclosure. This system involved the expansion of the coolant within the chamber into an auxiliary volume member (which may be a further adsorption pump) so as to effectively pre-cool the coolant prior to the use of the main adsorption pump. Effectively this produced a lower starting temperature and thereby improved the operational period of the system.
The abovementioned system as disclosed in EP1387133A is particularly advantageous over the prior art although in some circumstances, such as where extremely stable conditions are required, the operation of the valve (such as valve 8 in FIG. 1 thereof) causes mechanical vibrations, which is disadvantageous. There is a further desire, in addition to overcoming this problem, to reduce the cost of manufacture of the apparatus, to simplify its operation and to increase its operational reliability. It is these problems, among others, that are addressed by the present invention.